Elastomeric ethylene/α-olefin copolymer, inter alia includes both the copolymer EPM (ethylene-propylene monomers) as well as the interpolymer EPDM (ethylene-propylene diene M-rubber).
Elastomeric ethylene/α-olefin copolymer is produced commercially mainly in a solution polymerization process and slurry polymerization process. In the solution process, the reaction is carried out in an inert solvent, typical solid content 5-14 wt %. In the slurry process, the reaction is carried out in a diluent, the polymer is insoluble in the reaction medium. Typical solid content varies between 20 and 40%.
In an elastomeric ethylene/α-olefin copolymer polymerization, the reaction mixture typically comprises the elastomeric ethylene/α-olefin copolymer, diluent, whereby the term organic diluent generally encompasses diluting or dissolving organic chemicals which are liquid under reaction conditions, residual monomers and catalyst residues.
Downstream the reactor system, the reaction is “killed”, unreacted monomers, preferably volatile monomers are removed typically at reduced pressure via flashing and then the rubber needs to be separated from it's diluent/heavies. In the so-called “wet finishing” process, the viscous cement (solution process) or organic “slurry” (slurry process) is pumped into a agitated vessel partly full of boiling water: the diluent/heavies flash off and together with water vapor, pass overhead to a condenser and to a decanter for recovery and re-use.
The water is containing typically at least one anti-agglomerant: typical applied anti-agglomerants: carboxylic acid salts of multivalent metal ions, nonionic surfactants and layered silicate, in particular talcum, preferable in the form of 3MgO.4SiO2.H2O.
As a result of this operation a slurry of elastomeric ethylene/α-olefin copolymer particles in hot water is obtained, that needs to be dewatered and dried.
The isolated rubber particles may then be treated with additional auxiliary agents like anti-agglomerant, in particular with fatty acid salt of a multivalent metal ion, in particular with calcium stearate or zinc stearate, are then dried, baled and packed for delivery.
The anti-agglomerant ensures that in the process steps described above the elastomeric ethylene/α-olefin copolymer particles stay suspended and show a reduced tendency to agglomerate.
In the absence of an anti-agglomerant the naturally high adhesion of elastomeric ethylene/α-olefin copolymer would lead to rapid formation of a non-dispersed mass of rubber in the process water, plugging the process and leading to fouling.
The fundamental disadvantage of fatty acid salts of a multivalent metal ion, in particular calcium stearate and zinc stearate which are normally added later on before the dryer for friability properties, is their chemical interaction with elastomeric ethylene/α-olefin copolymer cure systems, for example causing slower cure times in resin cured compounds in particular those containing isoprene-iosolefin-elastomers. In addition, for EPM or its functionized derivatives as petroleum additives in particular haziness is caused by such auxiliary agents, like talcum.
Therefore, there is still a need for providing a process for the preparation of elastomeric ethylene/α-olefin copolymer particles in aqueous media having reduced or low tendency of agglomeration and in particular avoiding the problems described above.